CPX synergizes with cytarabine to induce cell death in leukemia cells. The effects of different concentrations of CPX in combination with cytarabine on the viability of OCI-AML2 cells were measured by MTS assay after 72 hours of incubation. Data were analyzed with Calcusyn software. Combination index (CI) versus fractional effect (FE) plot showing the effect of the combination of CPX and cytarabine. CI < 1 indicates synergism. One of 2 representative isobologram experiments performed in triplicate is shown.